1. Field of the Invention
The present invention relates to a spin-valve film, a magnetoresistance-effect device and a magnetoresistance-effect magnetic head.
2. Description of the Related Art
A magnetoresistance-effect magnetic head (hereinafter called an "MR head") is a reproduction-only magnetic head incorporating a magnetoresistance-effect device (hereinafter called an "MR device") which serves as a magnetization sensing device. The magnetoresistance-effect magnetic head has been put into practical use in a hard disc drive or the like. Since the recording density has been raised in recent years, a macro magnetoresistance-effect device incorporating a spin-valve film has been employed, the spin-valve film being a film which serves as an MR device for use in an MR head. The spin-valve film is formed by laminating a free layer structured such that the direction of the magnetization is to be changed by an exerted external magnetic field; a non-magnetic layer; a fixed layer fixed in which the direction of magnetization is to be directed to a substantially predetermined direction; and an antiferromagnetic layer.
To furthermore raise the recording density by using the MR head incorporating the spin-valve film, a high output from a narrow track is required. As a means for raising the output, reduction in the thickness of each of the films which constitute the spin-valve film is sometimes employed. If the thickness is reduced excessively, scattering depending on the spin from which the magnetoresistance effect can be obtained inhibited. Heat treatment is sometimes performed in the manufacturing process. If the thickness of each film constituting the spin-valve film is reduced, thermal stability of the spin-valve film deteriorates.
FIG. 1 shows the relationship between outputs of two types of spin-valve films having free layers, which constitute the spin-valve films and which have different thicknesses, and temperatures at which the heat treatment is performed. As can be understood from FIG. 1, a first spin-valve film having a free layer having a reduced thickness such that Ta/NiFe (2.5 nm)/CoFe (2.5 nm) enabled high outputs to be obtained as compared with a second spin-valve film having a thick free layer Ta/NiFe (5 nm)/CoFe (2.5 nm). As the temperature, at which the heat treatment is performed, is raised, the difference between the outputs of the two spin-valve film is reduced.
If the thickness of each layer constituting the spin-valve film is reduced as described above to raise the output immediately after the spin-valve film has been formed, the difference in the output is reduced after the heat treatment has been performed.
To obtain a high output even after the heat treatment has been performed, the output which is realized before the heat treatment is performed must be raised such that the thickness of each of the films constituting the spin-valve film is not reduced. As an alternative to this, the thermal stability of the spin-valve film must be improved. Under the present circumstances, any specific method cannot be provided.